Among resins, liquid crystalline polyesters exhibit favorable molding processability, have high levels of heat resistance and strength, and provide excellent insulating properties, and are therefore used as materials for electrical and electronic components and optical components.
With liquid crystalline polyesters, the molecular chains align readily along the flow direction during molding, and anisotropy tends to develop in the molding shrinkage rate and the mechanical properties between the flow direction and the direction perpendicular thereto. As a result, in order to reduce this anisotropy, fillers of various shapes, including fibrous fillers and plate-like fillers, are mixed into the resin.
On the other hand, when a fibrous filler is mixed with a liquid crystalline polyester, in order to obtain the desired levels of fluidity, moldability and molded article strength, it is preferable that the average fiber length of the filler is controlled. In particular, in order to obtain a molded article with improved levels of dust generation, which can occur due to dislodgement of the fibrous filler and the resulting generation of resin waste, it is important that the weight average fiber length of the fibrous filler in the molded article is shortened to a value within a prescribed range, such as a length of not more than 400 μm.
In this regard, Patent Document 1 discloses a method of obtaining a molded item by injection molding pellets obtained from a glass fiber-reinforced liquid crystalline resin composition, prepared by filling (A) 100 parts by weight of at least one liquid crystalline resin selected from among liquid crystalline polyester resins which form an anisotropic melt phase and liquid crystalline polyesteramide resins with (B) 5 to 300 parts by weight of glass fibers with an average fiber diameter of 3 to 15 μm and subsequently performing melt-kneading, wherein the weight average fiber length in the pellets is within a range from 0.02 to 0.55 mm, the proportion of glass fibers with a fiber length exceeding 1 mm is from 0 to 15% by weight of the glass fibers, and the proportion of glass fibers with a fiber length of not more than 0.1 mm is from 0 to 50% by weight of the glass fibers. The determination of the flow length during the injection molding and the shrinkage rate of the molded item is also disclosed.